Numerical Methods in Photonics

6.4.5  ABSORBING BOUNDARY CONDITIONS

In the MMs, the field is expanded on a discretized set of eigenmodes. Structures with closed or periodic boundary conditions, in the following referred to as non-open geometries, naturally feature discretized sets of guided and semi-radiation modes, as discussed previously in Section 2.7.3. These geometries are thus naturally compatible with the MMs.

However, when performing a simulation for an open geometry, the field should ideally be expanded on a discrete set of guided modes and on the continuous set of radiation modes. This continuous set represents an infinite number of modes, which cannot be stored in memory of a PC. We are thus forced to introduce a discretization of the continuous set of radiation ...